Systems and methods for generating hydrogen and magnetite from rock

ABSTRACT

Systems and methods for sequestering carbon, evolving hydrogen gas, producing iron oxide as magnetite, and producing magnesium carbonate as magnesite through sequential carbonation and serpentinization/hydration reactions involving processed olivine- and/or pyroxene-rich ores, as typically found in mafic and ultramafic igneous rock. Precious or scarce metals, such nickel, cobalt, chromium, rare earth elements, and others, may be concentrated in the remaining ore to facilitate their recovery from any gangue material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 63/203,814, filed Jul. 30, 2021, the entire contents ofwhich are incorporated herein by reference.

FIELD OF THE DISCLOSURE

One or more embodiments of this disclosure generally relate to systemsand methods that produce hydrogen, generate magnetite, and/or deriveadditional desired products from ores containing olivine or pyroxene(such as mafic and/or ultramafic rocks) through pre-selected chemicalprocesses. In one or more embodiments, the systems and methodsfacilitate carbonization and/or serpentinization/hydration reactionsinvolving olivine- and pyroxene-rich ores in order to sequester carbondioxide, liberate hydrogen, generate magnetite and magnesite, and/orderive other desired products, including scarce metals, which are inmany cases critical to various green technologies (e.g., batteries,energy storage, photovoltaics) otherwise mined using carbon-intensivemethods.

BACKGROUND

The environmental impact of greenhouse gases, primarily carbon dioxide(CO₂) and methane (CH₄), has been the subject of much public debate overthe past several decades. More recently, self-imposed private-sectorinitiatives and government-mandated regulations to reduce the release ofgreenhouse gases into the environment have begun to be implemented. Inaddition to the capture and/or sequestration of carbon dioxide and othergreenhouse gases to mitigate their atmospheric release, much researchand development effort has been focused on the utilization ofalternatives to fossil fuel combustion for energy production in order toreduce the amount of carbon dioxide generated and/or that must becaptured and sequestered.

Hydrogen (H₂) gas holds promise as an energy source (e.g., as hydrogenfuel or through the use of green ammonia) and chemical feedstock (e.g.,methanol, ammonia, hydrocarbon fuels) that provides little-to-nogreenhouse gas emission upon combustion. Indeed, the combustion ofhydrogen gas yields just water as a reaction product. However, hydrogengas has traditionally been produced using fossil fuels (e.g., vianatural gas/methane conversion in a steam reformer), which yields thegreenhouse gas carbon dioxide as a reaction product. For example, in thesteam-methane reforming reaction mentioned, methane is reacted withsteam (i.e., water) to produce hydrogen gas and carbon monoxide. In asubsequent water-gas shift reaction, the carbon monoxide is furtherreacted with steam to produce carbon dioxide and additional hydrogengas. The hydrogen gas is subsequently separated from the carbon dioxidethrough pressure swing adsorption, membrane separation, or another gasseparation process. Thus, most hydrogen that is produced in refineryoperations, for example, produces greenhouse gases, which must becaptured and sequestered to yield meaningful benefit.

Alternatively, hydrogen gas may be generated by the electrolysis ofwater into hydrogen gas and oxygen. The hydrogen gas is subsequentlyseparated from oxygen through pressure swing adsorption, membraneseparation, or another gas separation process. Hydrogen production viaelectrolysis, or partial pyrolysis reactions, requires a substantialamount of electricity. While at least some of the required electricityfor hydrogen production via electrolysis and/or partial pyrolysisreactions may be obtained from renewable sources (e.g., wind, solar, andhydroelectric), in practice the majority of the electricity used forthis purpose has traditionally been, and continues to be, producedthrough the combustion of fossils fuels, which also produces greenhousegases.

The abiotic production of hydrogen gas is known to occur in certaingeological formations, e.g., at young oceanic crust near a mid-oceanicridge, as depicted in FIGS. 1A-1D. These natural reactions occur acrossa range of environmental conditions that include variable pH, oxygenfugacity, chemical composition, and pressure. Such reactions producevariable and complex mineralogy and chemistry but do not predictablyproduce any specific combination of reaction products. In fact, asgenerally illustrated in the cross-section photograph of FIG. 2 , rockdeposits 200 that may yield abiotic hydrogen often contain complexmixtures or layers of difficult-to-extract mineral phases, or will notproduce a desired product if other competing reactions are preferredbased on in situ geochemical conditions (e.g., variable redox potential(Eh), pH, pore water composition, gas chemical composition, andtemperature). For example, hydrogen production is highly variable innature and its occurrence greatly depends on pH, Eh, and other aspectsof fluid geochemistry in pore spaces and at mineral surfaces. Thus, thecomplex kinetics of reaction phases and the occurrence of competingreactions in natural conditions (e.g., circumneutral pH, variable oxygenfugacity, and variable pore water chemistry) govern the products yieldedby these naturally occurring reactions. Certain geological formationsand/or the rocks thereof are also known to contain minerals that areconducive to reaction with carbon dioxide under certain conditions toform carbonated mineral phases, e.g., carbonates.

BRIEF SUMMARY

FIG. 3 provides a map that highlights the example locations of selectedsuitable and/or robust deposits of mafic and ultramafic rock around theworld. Olivine- and pyroxene-bearing ores may be found in such maficand/or ultramafic formations. As can be understood from FIG. 3 , sourcesof mafic and ultramafic igneous rocks may be found in many locations andare quite plentiful, accounting for at least 10% of the continentalcrust of the Earth, which illustrates the global applicability ofsolutions described herein. More recently, such sources of mafic andultramafic igneous rock have garnered interest for their potentialexploitation to sequester (mineralize) carbon dioxide in carbonatemineral phases. However, despite significant prior work on carbonsequestration, there is considerable debate about the best mechanisticreactions and optimized rates for carbon mineralization. As such, theeconomic viability of these processes has not been fully developed, norhas the hydrogen generation and carbon sequestration capacity of maficand ultramafic rocks been realized. Moreover, no economic use has beenidentified for the fine-grained carbonated mineral phases that resultfrom carbonization reactions. Rather, proposals have recommended suchcarbonated mineral phases be used as fill or dumped in oceans or lakes).

Despite the theoretical potential for such geological formations and/orthe ores thereof to be exploited for geological hydrogen or otherproducts, and for potential carbon sequestration, the processes andkinetics of these reactions has not been rigorously evaluated noroptimized. Further, processes for the production of hydrogen from thesegeological formations without the occurrence of alternative, andsometimes deleterious, mineral phases (e.g., serpentine, such asantigorite, asbestos) have not been developed. Accordingly, Applicanthas recognized a need for systems and methods that exploit certaingeological formations and/or the ores thereof to liberate hydrogen,generate magnetite and magnesite, and/or derive other desired products,such as scarce/critical metals from geological formations that includeolivine- and pyroxene-rich ores, and in addition, sequester carbondioxide in magnesite or other mineral phases.

The disclosure herein provides one or more embodiments of systems andmethods for sequestering carbon, evolving hydrogen gas, and producingmagnetite as well as magnesite from olivine- and pyroxene-bearing ores.In addition, precious or scarce metals, such as nickel, cobalt,chromium, and rare earth elements, may be concentrated in the remainingore, which facilitates their recovery.

In an example embodiment, a method is provided for sequestering carbonand producing hydrogen and magnetite. The method includes obtaining anore that containing olivine or pyroxene. The ore may be comminuted intosmaller size fractions, such as by crushing or grinding. The comminutedore may be introduced into a reactor that is operable at temperaturesabove ambient temperature and pressures above atmospheric pressure. Themethod may also include introducing carbon dioxide (or a mixture ofcarbon dioxide and other gases such as nitrogen (N₂), dihydrogen sulfide(H₂S), and sulfur dioxide (SO₂) into the reactor at a first temperatureabove ambient temperature for a first residence time to react at least aportion of the carbon dioxide with the ore. The method also includeslater introducing water into the reactor at a second temperature for asecond residence time to react at least a portion of the water with oneor more of the remaining ore to generate at least magnetite and hydrogengas. Reaction products, including hydrogen gas, magnesium carbonate(magnesite), magnetite, other reaction products, and any remaining oremay be removed from the reactor.

In another embodiment, a method is provided for sequestering carbon andgenerating hydrogen and magnetite from rock. The method includesobtaining an ore that olivine or pyroxene. As above, the ore may bebroken down into smaller size fractions, such as by crushing orgrinding. The ore is introduced into a first reactor that is operable ata first temperature above ambient temperature and pressures aboveatmospheric pressure. The method also includes introducing carbondioxide (or a mixture of carbon dioxide and other gases such as nitrogen(N₂), dihydrogen sulfide (H₂S), and sulfur dioxide (SO₂)) into the firstreactor at the first temperature for a first residence time to react atleast a portion of the carbon dioxide with the ore to generate at leastmagnesium carbonate. The remaining ore may be passed to a secondreactor. Reaction products from the first reactor may be separated fromthe remaining ore or may also be passed to the second reactor. Themethod also includes introducing water into the second reactor at asecond temperature for a second residence time to react at least aportion of the water with the remaining ore in the second reactor toproduce at least magnetite and hydrogen gas. Reaction products,including hydrogen gas, magnesium carbonate (magnesite), magnetite,other reaction products and any remaining ore may be removed from thesecond reactor.

In yet another embodiment, a system is provided for sequestering carbonand producing hydrogen and magnetite from rock. The system includes asource of ore that contains olivine or pyroxene. The system may includea crusher or grinder used to physically reduce the particle size of theore introduced therein from the source. The system may include a sieveused to receive the ore from the crusher and configured to allow oreparticles up to a pre-selected size to pass therethrough. The systemalso includes a reactor having an inlet that receives ore particles upto the pre-selected size from the sieve and at least one outlet. Thereactor also has at least one additional inlet through which one or moreof carbon dioxide or water may be introduced (and in some embodiments,the reactor may comprise two reactors: a first reactor having anadditional inlet through which carbon dioxide may be introduced, and asecond reactor having another additional inlet through which water maybe introduced). The reactor is operable at a first temperature for afirst residence time to react at least a portion of any received carbondioxide with the ore in the first reactor to generate at least magnesiumcarbonate. The reactor is also operable at a second temperature for asecond residence time to react at least a portion of any water thatenters the reactor through the at least one additional inlet with anyore within the reactor to generate magnetite and hydrogen gas. In one ormore embodiments, the system also includes a gas separator that isconnected to and in fluid communication with the at least one outlet ofthe reactor. The gas separator is configured to separate hydrogen gasfrom gases that exit the reactor through at least one outlet of thereactor.

Corresponding means for performing these various steps are set forthbelow.

The foregoing brief summary is provided merely for purposes ofsummarizing some example embodiments described herein. Because theabove-described embodiments are merely examples, they should not beconstrued to narrow the scope of this disclosure in any way. It will beappreciated that the scope of the present disclosure encompasses manypotential embodiments in addition to those summarized above, some ofwhich will be described in further detail below.

BRIEF DESCRIPTION OF THE FIGURES

Having described certain example embodiments in general terms above,reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale. Some embodiments may include fewer or morecomponents than those shown in the figures.

FIGS. 1A, 1B, 1C, and 1D illustrate cross-sectional representations ofyoung oceanic crust and associated structures positioned near atheoretical mid-oceanic ridge that may produce and/or host abiotichydrogen production.

FIG. 2 illustrates an example cross-section of serpentinized ultramaficrock.

FIG. 3 illustrates a map with locations of suitable olivine- andpyroxene-bearing localities throughout the world.

FIG. 4A provides an example flow diagram illustrating a sequence ofoperations performed by a system to enhance carbon dioxidesequestration, hydrogen gas evolution, and magnetite and magnesiteproduction using a single reactor, in accordance with some exampleembodiments described herein.

FIG. 4B provides an example flow diagram illustrating a sequence ofoperations performed by a system to enhance carbon dioxidesequestration, hydrogen gas evolution, and magnetite/magnesiteproduction using multiple reactors, in accordance with some exampleembodiments described herein.

FIG. 5 illustrates an example flowchart for enhancing carbon dioxidesequestration, hydrogen gas evolution, and magnetite/magnesiteproduction, in accordance with some example embodiments describedherein.

FIG. 6 illustrates an example flowchart for acquisition and preparationof source rock for reaction, in accordance with some example embodimentsdescribed herein.

FIG. 7 illustrates an example flowchart for processing rock remainingfollowing any carbon dioxide and/or water reactions, in accordance withsome example embodiments described herein.

DETAILED DESCRIPTION

Some example embodiments will now be described more fully hereinafterwith reference to the accompanying figures, in which some, but notnecessarily all, embodiments are shown. Because inventions describedherein may be embodied in many different forms, the invention should notbe limited solely to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will satisfy applicablelegal requirements.

Overview

Applicant recognized that despite the significant theoretical potentialof mafic and/or ultramafic igneous rocks (or, more broadly, olivine- andpyroxene-bearing ores, such as those with elevated iron content), asdescribed above, to serve as geological sources for economic geologicalhydrogen, to be exploited as natural sources and catalysts for hydrogenand magnetite production, and to be exploited for carbon sequestration,the optimal processes and kinetics for these reactions have not beenrigorously evaluated nor optimized. Specifically, process steps toenhance both carbon sequestration and the production of hydrogen,magnetite, magnesite, and/or other minerals from these types ofrocks—without the formation of alternative (and sometimes deleterious,e.g., serpentine, asbestos) mineral phases—have not been developed.

Further, Applicant is unaware of any prior attempts to use an optimizedchemical process of carbon mineralization to enhance the kinetics ofhydrogen and magnetite production, or to regulate the chemical speciesof the resulting reaction products (e.g., prevent the formation ofserpentine and asbestos).

In various embodiments disclosed herein, carbon dioxide may besequestered and hydrogen, magnetite, and other scarce metals may beproduced economically (and with a neutral to net-negative carbonfootprint) using olivine- and pyroxene-rich ores through sequentialcarbonation and serpentinization reactions in a controlled environment.Thus, Applicant has developed an engineering process that employssequential reactions to exploit the potential for olivine- andpyroxene-rich ores to both sequester carbon dioxide dominantly asmagnesite or other carbonate minerals, as well as liberate hydrogen,magnetite, and/or other desirable minerals/scarce metals. Applicantfurther recognized that additional process steps applied to the olivine-and pyroxene-rich ores may enhance the concentration and recovery ofprecious or scarce metals (e.g., nickel, cobalt, chromium, lithium, andrare earth elements), which are needed for renewable energy and energystorage, among other uses.

Applicant discovered that the serpentinization reaction process can beadvantaged such that the chemical activity and commensurate rates ofreactions between water and fayalite and/or ferrosilite may be enhancedby first removing a significant component of forsterite from the olivinemineral phase and increasing the comminution of mineral grains byinducing the described chemical reactions. In this way, the fayaliteand/or ferrosilite in the igneous rock is concentrated and/or becomesless obscured by adjacent minerals, e.g., forsterite. This processbenefits the reaction in two ways: first, by enhancing the surface areaof fayalite and/or ferrosilite exposed for the reaction; and second, bypre-concentrating the reactant (iron-rich olivine (fayalite) or pyroxene(ferrosilite)) of choice. Thus, in one or more embodiments, forsteriteand/or enstatite are at least partially removed prior to reacting thefayalite and/or ferrosilite with water.

Some primary differentiators that demonstrate the value of example exsitu engineered embodiments that produce hydrogen, magnesite, magnetite,and critical metals via this pathway include: 1) the immense geologicalscalability of such embodiments once the “serpentinization” processesare optimized to produce the desired products (hydrogen, magnetite,scarce metals), as opposed to alternative mineral phases such asserpentine, asbestos, etc.; 2) the potential to permanently andverifiably sequester CO₂ in a mineralized form and hence producehydrogen, magnetite, and scarce metals in a carbon-negative process; and3) the price point of potentially scalable “green” or “golden” hydrogen(i.e., carbon negative hydrogen), magnetite, and scarce metals, whichcan be greatly offset by considering other values streams generatedusing the quarrying concept (i.e., the sale of aggregate or higher valueutilization of magnesite).

Although a high level explanation of the operations of exampleembodiments has been provided above, specific details regarding theconfiguration of such example embodiments are provided below.

Serpentinization and Carbonation Reactions

The disclosure herein provides one or more embodiments of systems andmethods that facilitate the production of hydrogen, magnetite, and/orother desired minerals through serpentinization reactions involvingolivine- and pyroxene-rich ores generally found in mafic and/orultramafic igneous rock, or of any other rock assemblages containingsuch olivine- and pyroxene-rich ores. Table 1, provided below, givesrepresentative serpentinization reactions involving fayalite (Fe₂SiO₄)and/or ferrosilite (Fe₂Si₂O₆). Fayalite is a mineral phase that is theiron-rich endmember of the olivine solid solution series and is abundantin olivine-rich ore. Ferrosilite is the iron-rich endmember of theorthopyroxene solid solution series and is associated with pyroxene-richore. Fayalite and ferrosilite are commonly found together in mafic andultramafic igneous rocks. Under certain conditions, water reacts withfayalite and ferrosilite to generate magnetite (Fe₃O₄), silica (SiO₂),and hydrogen gas (H₂) in the appropriate stoichiometric ratios. In eachcase, two moles of hydrogen gas are produced from three moles of eitherfayalite or ferrosilite mineral.

TABLE 1 Hydrogen-Generating Serpentinization Reactions SerpentinizationReactions Moles of Igneous Moles Mineral Mineral Phase SerpentinizationReaction Mineral of H₂ Olivine Fayalite 3 Fe₂ + 2 H₂O → 2 Fe₃O₄ + 3SiO₂ + 2 H₂ 3 2 Pyroxene Ferrosilite 3 Fe₂Si₂O₆ + 2 H₂O → 2 Fe₃O₄ + 6SiO₂ + 2 H₂ 3 2

In one or more embodiments, the disclosed systems and methods may alsofacilitate the sequestration of gaseous carbon dioxide as mineralizedcarbonates through carbonation reactions involving the magnesium-richendmember of olivine- and pyroxene-rich ores found typically in maficand/or ultramafic rock. Table 2, provided below, gives representativecarbonation reactions involving forsterite (Mg₂SiO₄) and enstatite(Mg₂Si₂O₆), as well as illustrating the potential for carbonation duringreaction with antigorite (Mg₃Si₂O₅(OH)₄) that can be formed as anaccessory mineral phase in natural systems in which fluid conditions arenot idealized for the formation of magnesite. Forsterite is a mineralphase that is the magnesium-rich endmember of the olivine solid solutionseries associated with olivine-rich ore. Enstatite is a mineral phasethat is the magnesium-rich endmember of the orthopyroxene solid solutionseries associated with pyroxene-rich ore. Antigorite is an examplemineral phase that is associated with serpentine. Under certainconditions, carbon dioxide reacts with forsterite and enstatite, and/orother accessory mineral phases (e.g., antigorite) to generate at leastmagnesium carbonate (MgCO₃) and silica (SiO₂) in appropriatestoichiometric ratios. The reaction of antigorite with carbon dioxidefurther yields a stoichiometric quantity of water and is shown toillustrate serpentinization reactions that occur in natural systems inwhich pH, Eh, temperature, pressure, and fluid chemistry cannot beoptimized. In the case of the idealized carbonization reaction involvingforsterite and enstatite, two moles of carbon dioxide gas are convertedto magnesium carbonate (magnesite) per mole of either forsterite orenstatite mineral.

TABLE 2 Carbon-Sequestering Carbonation Reactions DecarbonationReactions Moles of Mineral Igneous Moles Mineral Phase DecarbonationReaction Mineral of CO₂ Olivine Forsterite Mg₂SiO₄ + 2 CO₂ → 2 MgCO₃ +SiO₂ 1 2 Pyroxene Enstatite Mg₂Si₂O₆ + 2 CO₂ → 2 MgCO₃ + 2 SiO₂ 1 2Serpentine Antigorite Mg₃Si₂O₅(OH)₄ + 3 CO₂ → 3 MgCO₃ + 2 SiO₂ + 2 H₂O 13

In nature, and as previously described, the above-describedserpentinization and carbonization reactions occur, but only as a subsetof a variety of reactions occurring across a range of environmentalconditions in the subsurface or at surface conditions of the earth. As aresult, the environmental conditions are often variable and reactionskinetics and pathways are far from ideal. Accordingly, natural reactionsare based on the variable (and often dynamic, i.e., changing with time)pH, oxygen fugacity, temperature, pore water chemical composition, gaschemical composition, and pressure found in nature, specifically in thesubsurface. The multitude of reactions and potential pathways for thosereactions occurring in nature lead to the formation of variable andcomplex chemistry and assemblages of minerals, but do not predictablyproduce any specific combination of usable reaction products. Instead,natural systems, which evolve through time and under varying reactionconditions produce complex (and often heterogeneous) complexes ofvarying mineral assemblages and products of reactions that did notfollow the idealized reactions described above, or are slower to reachthermodynamic equilibrium.

With respect to olivine and pyroxene mineralogy and chemistry, olivineis a solid solution series (X₂SiO₄, where X=Mg²⁺ or Fe²⁺) between amagnesium silicate (forsterite) and an iron silicate (fayalite) andpyroxene (i.e., orthopyroxene) is a solid solution series (X₂Si₂O₆,where X=Mg²⁺ or Fe²⁺) between a magnesium silicate (enstatite) and aniron silicate (ferrosilite). In the olivine-rich deposits of interest,fayalite and ferrosilite are usually the minor constituent and typicallyrange in concentration from 6% to 20%, with the lower rangeconcentrations appearing more commonly in nature. Consequently, thethermochemical activities of fayalite and ferrosilite are relatively lowcompared to those of the forsterite or enstatite, respectively. Thus, ifthe olivine or pyroxene obtained from a quarry is crushed and reactedwith water at favorable reaction conditions (i.e., controlled fortemperatures, pressures, Eh, pH, and fluid composition, then aserpentinization reaction will proceed at a relatively low rate due torelatively low thermochemical activity and commensurately low rates ofreactions with fayalite or ferrosilite. Nevertheless, when completed,the reaction produces magnetite, silica, and hydrogen (from the reactionof fayalite or ferrosilite with water) may be separated (magnetically orgravimetrically) from forsterite, enstatite, or magnesite. The mixtureof olivine (forsterite and fayalite) and pyroxene (enstatite andferrosilite) minerals, however, constitutes an almost an “ideal” mixturethat is exceedingly rare in natural systems. However, in an idealmixture, the chemical activity varies linearly with the mole fractionand is roughly equal to the mole fraction. Thus, the chemical activityand reaction rate can be enhanced by pre-concentrating the abundance ofolivine and pyroxene from the bulk ore and specifically the abundance ofthe iron-rich endmembers of both the olivine and pyroxene solid solutionseries.

Ex Situ Sequestration of Carbon Dioxide and Generation of Hydrogen

In various embodiments contemplated herein, carbon dioxide may bemineralized, and hydrogen, magnesite, magnetite, and critical metals maybe produced economically (and with an overall neutral to net-negativecarbon footprint) by an engineered system that causes sequentialreactions in the manner shown in the flow diagrams illustrated in FIGS.4A, 4B, and described in connection with the flowcharts provided inFIGS. 5, 6, and 7 .

FIG. 4A illustrates a flow diagram of one embodiment 400′ of a systemfor enhancing the production of hydrogen gas and magnetite from rockthat contains a mixture of olivine (e.g., fayalite and forsterite) andpyroxene (e.g., ferrosilite and enstatite) minerals. A source ofolivine- and/or pyroxene-rich ores 402 may be fed or introduced into acrusher or grinder 406 that reduces the size of the received ore intosmaller size fractions. In one or more embodiments, a washer 404 mayoptionally be used to wash the ore with water or a mildly acidicsolution to remove any contaminants therefrom and prepare the ore forcarbonation reactions. The crushed or ground rock is then introducedinto a sieve 408 or other such separator that segregates the rock intopre-selected particle ranges. In one or more embodiments, the sieves orgrates thereof are sized to pass 150-, 80-, and even 45- micron grains,although different sizing can be utilized. In at least one embodiment,the comminuted rock is a powder or has a powder-like particle sizerange. Rock that does not pass through the sieve may be returned to thecrusher or grinder 406 via a recycle loop 410 to be reduced further insize. The subset of the rock having particles within a pre-selectedparticle range of the sieve 408, e.g., 150-micron, 80-micron, 45-micronor any size therebetween, is then fed or introduced into a reactor 412.

The reactor 412 may be a rotary kiln, a toroidal fluidized bed, afluidized bed, or another reactor known to those skilled in the art. Thereactor 412 may have an inlet that receives ore (or ore particles) atleast one outlet, from which any remaining ore may be removed followingreaction within the reactor 412. The reactor 412 may further have atleast one additional inlet through which one or more of carbon dioxideor water can be introduced into the reactor 412. The reactor 412 may beoperable at a first temperature for a first residence time to reactcarbon dioxide that enters the reactor 412 through the at least oneadditional inlet with ore disposed within the reactor 412 to generatemagnesium carbonate. The reactor 412 may further be operable at a secondtemperature for a second residence time to react water that enters thereactor through the at least one additional inlet (which may be the sameinlet by which carbon dioxide enters the reactor 412 or a differentinlet) with ore disposed within the reactor 412 to generate magnetiteand hydrogen gas.

In a first reaction step, carbon dioxide is introduced into reactor 412with the crushed/ground rock. Water (approximately 10 liters of waterper kilogram) may be applied (sprayed or washed) to the crushed/groundrock by washer 404 either before or after placement of the rock into thereactor 412. The wetting of the powdered rock with water allows for thedissolution of gaseous CO₂ to carbonic acid (H₂CO₃) on the wet surfacesof the mineral grains, which enhances the reactivity of the carbondioxide with the forsterite mineral found therein. In at least oneembodiment, the pH of the water applied to the comminuted rock may bebetween about 4.8 to about 6.5. Water in this pre-selected pH rangefurther enhances the reaction between the carbon dioxide and theforsterite mineral. During this first reaction step, the reactor isoperated at a pre-selected temperature (>90° C.) and pressure (greaterthan approximately five bars) to facilitate the carbonation reactionwith respect to the forsterite mineral found in the rock. In one or moreembodiments, the reactor 412 is operated at a temperature of betweenabout 100° C. to about 400° C. and at a pressure of between about fiveand up to at least 100 bars (e.g., about 40, 50, 75 or even 100 bars);note the upper limit of pressure can be extended to considerably higherpressures if the reactor 412 and associated components are able towithstand such pressures. Increasing pressure in this fashion willproduce a corresponding enhancement of the carbonation reaction beingprompted at this stage of the process. In other embodiments, theoperating pressure of the reactor 412 may be as low as 35 bars, as lowas 30 bars, as low as 25 bars, as low as 20 bars, as low as 15 bars, aslow as 10 bars, as low as 5 bars, or even lower (˜1 bar), and may stillprompt the intended carbonation reactions, albeit at commensuratelylower rates of reaction. As provided in Table 2 above, the reaction ofcarbon dioxide with the forsterite (Mg₂SiO₄) produces magnesiumcarbonate (MgCO₃) and silicon dioxide (SiO₂) as reaction products. Inthis way, the forsterite mineral of the mafic and/or ultramafic rock isused to permanently sequester CO₂ in the form of an insoluble magnesiumcarbonate mineral lattice, which is a solid that that can be useful as araw material, placed in a landfill, ocean, lake, or otherwise easilystored. By reacting the crushed/ground rock containing the forsteritewith carbon dioxide at favorable conditions of temperature, pressure,Eh, and pH, the forsterite can be altered to magnesite followingreaction with carbon dioxide.

It will be understood that, although this first reaction step favorablyenhances the comminution of source rock and better prepares anyremaining rock for the second reaction step described below, someembodiments may not perform this first reaction step, and instead maysimply comminute the source rock, which itself prepares the source rockfor the second reaction step, as illustrated by way of example in theExample Implementation section below. Of course, in other embodiments,the source rock may not need to undergo an initial comminution step, butmay instead simply be initially processed using the first reaction stepdescribed herein, which itself fosters comminution of the source rockand thus prepares it for more effective reaction in the second reactionstep described below. Both comminution of the source rock and thecarbonation reactions occurring during the first reaction step favorablydispose any remaining rock for the section reaction step below;accordingly, various combination of comminution and the first reactionstep may be employed in various scenarios based on the desired resultsof a given implementation.

In a second reaction step, water is thereafter introduced into reactor412 with the crushed/ground rock, which may in some embodiments stillcontain the magnesium carbonate and silicon dioxide from the firstreaction step, the fayalite and/or ferrosilite minerals in the originalcrushed/ground rock, and any other minerals/ores found in the originalcrushed/ground rock. In some embodiments, magnesium carbonate andsilicon dioxide from the first reaction step can be separated from theresidual iron silicate phases based on their respective densities. Inone or more embodiments of these processes, the water that is added tothe reactor 412 may have a low oxygen fugacity (e.g., it may be obtainedfrom municipal wastewater treatment, groundwater, geothermal water, minewaters, another industrial water source, or by reacting a municipalwater (i.e., “tap water”) over a bed of copper at temperatures exceeding125° C., or by another mechanism) and a pH of between about 8.3 andabout 11.1 (with the specified pH being artificially attained, such asby adding sodium bicarbonate to the water, or naturally obtained, suchas where the water with such pH range may be found in certain sources ofwater and wastewater). During this second reaction step, the reactor isoperated at a pre-selected temperature and pressure (˜1 to 20 bars) tofacilitate the serpentinization of the fayalite and/or ferrosiliteminerals in the rock. In one or more embodiments, the reactor 412 isoperated at a temperature in the range of between about 80° C. and about400° C. As provided in Table 1 above, the reaction of water with thefayalite (Fe₂SiO₄) and/or ferrosilite (Fe₂Si₂O₆) produces hydrogen gas,variable mixtures of nitrogen (N₂), carbon dioxide (CO₂), silicondioxide, and magnetite (Fe₃O₄) as reaction products. The molecular andisotopic composition of hydrogen formed during this ex situ process willbe determined by the temperature conditions of the reaction (e.g., —175°C.) and the composition of the initial water, wherein the fractionationfactors (a) between H₂O and H₂ follow the fractionation factors observedfor standard geothermometers. The hydrogen gas, along with any othergases in the reactor 412, such as unreacted carbon dioxide (CO₂), sulfurdioxide (SO₂), or dihydrogen sulfide (H₂S) or inert gases (e.g.,nitrogen (N₂), argon (Ar) from the first reaction step, are passed to agas separator 414. The gas separator 414 may be a membrane unit, apressure swing adsorption, or a cryogenic separation unit that canseparate the hydrogen gas from other gases, e.g., atmospheric gases,that may also be present in the reactor 412. The gas separator 414 maybe connected to and in fluid communication with at least one outlet ofthe reactor 412 and configured to separate hydrogen gas from gases thatexit the reactor 412 through the at least one outlet.

In at least one embodiment, gases that may be present in the reactor 412prior to the second reaction may be evacuated prior to the secondreaction, such as by pulling a vacuum on the reactor 412. Without thesecontaminant gases in the reactor 412 (e.g., N₂ or CO₂), the hydrogen gasthat is formed as a result of the serpentinization reaction with watermay be the only gas present after the second reaction step. In suchcase, the gas separator 414 may not be needed to segregate the hydrogengas as a product. After the second reaction step, the magnesiumcarbonate, silicon dioxide, magnetite, and any remaining rock/unreactedore may be removed from the reactor 412. In some embodiments, magnesiumcarbonate (i.e., magnesite) and silicon dioxide (i.e., quartz) may beseparated from iron silicates and other mineral phases before thematerial is placed in reactor 412. The magnetite, which represents avaluable product/feedstock for the iron industry (with particular valuein direct reduced iron manufacturing), may be recovered from themagnesium carbonate, silicon dioxide and any remaining rock/ore by, forexample, magnetic separation or other density separation techniques. Amagnetic separator 416 may be used to selectively attract the magnetitethrough the use of one or more magnets and thereby physically remove themagnetite from the other non-metallic ore. In one or more embodiments,the solid products, e.g., the magnetite, magnesium carbonate, silicondioxide, and any remaining, unreacted ore/rock may be further crushed orground (not shown in FIG. 4A) to facilitate the removal of magnetiteparticles from the other solids in the magnetic separator 416 or conductsecondary recovery of other minerals or metal-rich phases. The separatedhydrogen gas from gas separator 414 and the magnetite recovered via themagnetic separator 416 are valuable products whose production andrecovery from mafic and/or ultramafic rock are enhanced by the disclosedsequential carbonization and serpentinization reactions disclosedherein.

The remaining magnesium carbonate (in which the carbon is permanentlysequestered in the mineral phase), silicon dioxide, and any unreactedrock/ore may be used as an aggregate material and/or placed in landfillor otherwise disposed of. In one or more embodiments, the magnesiumcarbonate and silicon dioxide may be separated (based on densityseparation techniques such as heavy liquids or other gravity separation,or sluicing) and removed from the remaining rock/gangue (gangue:collection of accessory mineral phases such as phosphates, sulfides,aluminum oxides, etc.) materials. As further discussed below, magnesiumcarbonate (or magnesite) is useful in the manufacturing ofpharmaceuticals, agricultural lime, and fertilizers (to neutralizeacidification caused by fertilizer use), ceramics and ceramic brick, andas flux used in iron and steel manufacturing. Magnesite may also be usedas a partial lime substitute to enable lower carbon emissions thatresult from the lower temperatures required to make magnesium oxide(MgO) as compared to calcium oxide (CaO) for cement manufacturing.Further, magnesite can be used as a carbon negative concrete filler andcement or aggregate substitute in concrete.

In one or more embodiments, rather than landfilling or otherwise usingthe bulk of the magnesium carbonate, silicon dioxide, and any unreactedrock/ore, the rock and/or gangue material from the first reaction phaseis further processed to separate and remove specific valuable componentstherefrom. For example, elevated concentrations of certain preciousmetals (e.g., nickel, cobalt, chromium, and rare earth elements) inmafic and ultramafic rocks are further concentrated in this “slag”material. In at least one embodiment, highly elevated metal enrichments,that include but are not limited to phosphates, aluminum oxides,precious metals, and other mineral gangue may be separated from theremaining rock/ore by, for instance, heavy liquid separation or othergravity separation, or sluicing in a separator 418. Through gravityseparation, the various metals and other valuable components are groundinto fine particles and separated based on their individual specificweights.

As illustrated in FIG. 4A, the first and second reactions can both occurin the same reactor 412, which may be a rotary kiln, fluidized bed,toroidal bed, or other reactor as described previously, in which casethe reactions may be run sequentially, and all products separated at thecompletion of both reactions. In one or more embodiments (not shown inFIG. 4A), the reaction products (i.e., magnesium carbonate and silicondioxide) may be separated after the first reaction step and prior to thesecond reaction step using established density separation techniquessuch as heavy liquid separation or other gravity separation, orsluicing. In other embodiments, as shown in FIG. 4A, the reactionproducts remain in the reactor during the second reaction step. Even ifthe reaction products are not physically separated, the thermochemicalactivity and reaction rates of fayalite and/or ferrosilite will increaseaccording to the newly exposed surface area of fayalite and/orferrosilite minerals. In other words, the reactivity of theserpentinization reactions with respect to the fayalite and/orferrosilite minerals will proceed according to the now higher molarfraction of fayalite and/or ferrosilite in the solid solution (i.e., thenumber and/or extent of alternative side reactions has been reduced).With respect to the upper limit of the fully separated (e.g., usingestablished density separation techniques such as heavy liquidseparation or other gravity separation, or sluicing) or exposed fayaliteand/or ferrosilite, the thermochemical activity of the powdered materialshould approach unity of the pure phase mineral, or mixtures of fayaliteand/or ferrosilite mineral phases. Thus, the first reaction stepinvolving the reaction of the forsterite with carbon dioxide increasesthe thermochemical driver for the second reaction step, which is theserpentinization/hydration reaction of the fayalite and/or ferrosilitewith water, by reducing the availability of forsterite and increasingthe exposed surface area of fayalite and/or ferrosilite minerals. Theformer increases the kinetic rate by driving the thermochemical activitytoward that of a pure compound, while the latter enhances chemicalactivity by increasing the surface area available for reaction.

FIG. 4B illustrates a flow diagram of another embodiment 400″ of asystem of enhancing the production of hydrogen gas and magnetite from asource rock that contains a mixture including olivine (fayalite andforsterite) and/or pyroxene (ferrosilite and enstatite) minerals. Theflow diagram of FIG. 4B is similar to that of FIG. 4A, except that thefirst reaction step occurs in a first reactor 412′ and the secondreaction step occurs in a second reactor 412″. The first reactor 412′facilities the carbonation reaction between the forsterite mineral andcarbon dioxide. The crushed/ground ore of a uniform or pre-selectedparticle size range is passed from the sieve 408 or other particle sizeseparator into the first reactor 412′. Carbon dioxide is pumped into thefirst reactor 412′ in above stoichiometric ratios to facilitate thecarbonization reactions listed in Table 2. After the first reaction hasoccurred, the magnesium carbonate and silicon dioxide products, alongwith the unreacted fayalite and/or ferrosilite, and other remaining ore,are passed to the second reactor 412″.

Continuing with FIG. 4B, the second reactor 412″ facilitates theserpentinization reaction between the fayalite and/or ferrosilitemineral phases and water (or steam). The reaction products and remainingrock/ore from the first reactor 412′ are introduced into the secondreactor 412″. Water is pumped into the second reactor 412″ in abovestoichiometric ratios (>˜20 liters/kg of rock) to facilitate theserpentinization reactions listed in Table 1. After the second reactionhas occurred, the reactor gases, including the hydrogen gas evolvedduring the second reaction step, are passed or routed to a gas separator414, as described above with respect to FIG. 4A. Likewise, the solidreaction products, including magnesium carbonate, silicon dioxide,magnetite, as well as any unreacted ore/rock are passed to a magneticseparator 416, as described above with respect to FIG. 4B. Other thanthe use of two reactors 412′ and 412″ in place of one reactor 412, asdescribed above, the embodiments represented by FIGS. 4A and 4B aresimilar. It should be noted that the configuration of the system of FIG.4B provides a semi-continuous method in that the separate processvessels, e.g., reactors 412′ and 412″, are dedicated to differingportions of the method.

FIGS. 5, 6, and 7 illustrate flowcharts of various embodiments forenhancing the production of hydrogen gas, magnetite, magnesite, andscarce metal resources from mafic and ultramafic igneous rock thatcontains a mixture of olivine (fayalite and forsterite) and pyroxene(ferrosilite and enstatite) minerals. As previously disclosed inconnection with FIG. 3 , olivine- and/or pyroxene-rich ores may be foundin numerous locations around the world. At block 502, such olivine-and/or pyroxene-rich ore may be acquired from geological sitescontaining high concentrations of such rocks in one or more of theseareas. FIG. 6 illustrates this rock acquisition operation in greaterdetail. As shown at block 602, the olivine- and/or pyroxene-rich sourcerock may be acquired in any manner known to those skilled in the art,such as by underground mining, strip mining, quarrying, outcropquarrying, or the use of waste (i.e., mine tailings), etc. The sourcerock may be transported, e.g., by barge, train, truck, etc., to afacility to further process the rock. In one or more embodiments, thesource rock may be processed in proximity to the location where the rockis acquired. The source rock may be processed by crushing and/orgrinding the rock at block 606 into smaller size fractions. In additionto creating uniform or near uniform sizing, such comminution also helpsto expose the minerals, such as olivine (forsterite and fayalite) andpyroxene (enstatite and ferrosilite), that are contained within therock. If the rock is processed in proximity to the geological site fromwhich the rock originated, then the processed rock may then betransported to a facility having a system to further extract hydrogen,magnetite, and other valuable products from the ore according to amethod disclosed herein (not shown in FIGS. 5 and 6 ). At block 608, thecrushed and/or ground source rock may be further processed by sieving orotherwise segregating the rock according to size. In one or moreembodiments, the crushed and/or ground rock may be washed with water ora slightly acidic solution to clean the surfaces thereof of dust, dirt,or other contaminants. As illustrated at block 604, such washing may beconducted before the rock is crushed and/or ground and can also benefitfrom agitation.

The crushed and/or ground rock is then introduced into a reactor atblock 610 in which the rock is reacted with carbon dioxide and water toproduce magnesium carbonate and hydrogen gas, among other products, instoichiometric proportions via the carbonation reactions described inTable 2. The crushed/ground rock may be transported between andintroduced into the reactor at block 610 by conveyor, by machineryplacement, etc. A slightly acidic water solution, as previouslydescribed may be applied, e.g., by washing, spraying, or soaking, ontothe outer surfaces of the rock. Such application may be before or afterthe rock is deposited in the reactor. The air in the reactor, includingoxygen therein, may be evacuated from the sealed reactor with the rockdisposed therein (e.g., by applying a vacuum to the reactor) or purgedusing reaction gas (e.g., N₂) prior to commencing the reaction.Returning to FIG. 5 , block 504 describes that carbon dioxide (CO₂) isintroduced into the reactor to begin the first reaction phase. Thecarbon dioxide may be gaseous or supercritical as previously described.A greater-than-stoichiometric portion of carbon dioxide is added ascompared to the amount of rock (and specifically forsteriteconcentration therein) in the reactor in order to ensure that the carbondioxide does not limit the carbonation reaction and to benefit fromincreased reactivity that is observed to occur at elevated pressures ofCO₂ and/or super-critical CO₂. At block 504, the reactor is operated atone or more pre-selected temperatures and pressures, as described above,for a first residence time in order to sufficiently react the carbondioxide with the forsterite mineral to produce magnesium carbonate andsilicon dioxide reaction products. At the end of the first residencetime, the gas phase from the reactor may be evacuated by, e.g., applyinga vacuum or gas purging operation, to remove the excess unreacted carbondioxide and any other gases evolved via the carbonation reactions of thefirst reaction phase.

Continuing with FIG. 5 , at block 506, water is introduced to thereactor after the first residence time. In one or more embodiments, thewater is a low oxygen fugacity water that is prepared or obtained asdescribed in greater detail above. Again, a greater-than-stoichiometricportion of water (>˜20 liters/kg of rock) is added as compared to theamount of rock (and specifically fayalite and/or ferrosiliteconcentrations therein) in the reactor in order to ensure that the waterdoes not limit the serpentinization reaction. At block 506, the reactoris operated at one or more pre-selected temperatures and pressures, asdescribed above, for a second residence time in order to sufficientlyreact the water with the fayalite and/or ferrosilite minerals (nowhaving additional exposed surface area and more optimized chemicalactivity due to the first reaction phase) to produce at least hydrogengas and magnetite reaction products.

At block 508, the gas phase is removed from the reactor either during orat the completion of the second reaction phase. This gas phase, which isrich in hydrogen gas (and may contain small quantities of trace gases,e.g., N₂, Ar, CO₂) may be further purified through gas separator 414 (asshown in FIG. 4A and FIG. 4B). The gas separator 414 may be a pressureswing adsorption unit, a membrane separation unit, a cryogenicseparation unit, or any other gas separation unit known to those skilledin the art. If the gas phase was not evacuated from the reactor betweenthe first reaction phase and the second reaction phase, then some carbondioxide and/or other gases, e.g., reaction gases, may contaminate thehydrogen gas evolved in the reactor via the serpentinization reactionsof the second reaction phase.

At block 510, the remaining rock within the reactor may be furtherprocessed to remove the magnesium carbonate/magnesite, the ironoxide/magnetite, the silicon dioxide, any remaining ore and/or slagmaterial from the reactor. These operations are described in detail inconnection with FIG. 7 . Block 702 illustrates that the remaining rockin the reactor may be removed for further processing. Such removal mayinclude removal by mechanical machinery, which picks up, rakes, orgravity feeds the material from the reactor into a container or onto aconveyor. In particular, at block 702 the solid reaction products (i.e.,magnesite, magnetite, etc.), the remaining ore, and any slag materialmay be passed to a magnetic separator 416 (as shown in FIG. 4A and FIG.4B) in order to separate the magnetite from the other materials viaattraction of the magnetically susceptible iron oxide to a magneticfield (see block 704). The solid material removed from the reactor atblock 702 may undergo additional crushing and/or grinding in order tocreate a fine powder to facilitate removal of valuable componentsthereof (not shown in FIGS. 5 and 7 ). At block 706, any precious orscarce metals that are now more concentrated in the remaining ore and/organgue (collection of accessory mineral phases such as phosphates,sulfides, aluminum oxides, etc.) material after magnetite removal may beseparated and removed based on density separation techniques such asheavy liquid separation or other gravity separation, or sluicing; anexample of gravity separation using a gravity separator is shown in 480.Finally, as shown in block 708, the remaining rock, containing remainingmagnesium carbonate (in which the carbon is permanently sequestered inthe mineral phase), silicon dioxide, and any unreacted rock/ore may beused as an aggregate material and/or placed in landfill or otherwisedisposed of. As noted previously, in some embodiments the magnesiumcarbonate and silicon dioxide may be separated (based on densityseparation techniques such as heavy liquids separation, or other gravityseparation, or sluicing) and removed from the remaining rock/gangue(gangue: collection of accessory mineral phases such as phosphates,sulfides, aluminum oxides, etc.) materials for separate dispositioning.

FIGS. 5, 6, and 7 illustrates operations performed in various exampleembodiments. It will be understood that each flowchart block, and eachcombination of flowchart blocks, may be implemented by various means.The flowchart blocks support combinations of means for performing thespecified functions and combinations of operations for performing thespecified functions. In some embodiments, some of the operations abovemay be modified or further amplified. Furthermore, in some embodiments,additional optional operations may be included. Modifications,amplifications, or additions to the operations above may be performed inany order and in any combination.

Example Implementation

In one example embodiment, an ultramafic ore was reacted with carbondioxide to sequester the carbon in the magnesium carbonate mineral phaseand water to evolve hydrogen gas as well as produce magnetite. Theexample was conducted in three phases: 1) rock preparation; 2) waterpreparation; and 3) reaction process, each of which will be described ingreater detail below. As part of the analysis of the overall system andmethod, the composition of the ore (i.e., olivine (forsterite andfayalite) and pyroxene (enstatite and ferrosilite) minerals), thereaction conditions to which the ore was subjected, and thecharacteristics of the carbonation/serpentinization reaction productswere assessed. For instance, with respect to the ore composition, themass, mineralogy, and geochemical composition of the bulk rock wereevaluated by optical mineralogy, x-ray powder diffraction (XRD), andinductively coupled plasma mass spectrometry (ICP-MS) to evaluate theabundance of relevant constituents (e.g., fayalite, ferrosilite, FeO,MgO).

In the rock preparation phase, an ultramafic aggregate material thatincluded mostly rock particles of approximately 1 cm in size werecollected from four active quarries (namely, two quarries inPennsylvania, one in Virginia, and one in Kentucky). The ultramaficaggregate material was disaggregated (i.e., lightly crushed/comminuted)initially with a rock hammer and then with a Spex Ball mill. Thepowdered material was then sieved using grates arranged and designed topass 150-, 80-, and then 45-micron grains successively. This enabledexperimentation to be conducted on at least three different grainssizes. Another material—a homogenized olivine mineral—was also purchasedfrom a scientific supplier in California. This olivine material, whichwas homogenized for size and composition, had a uniform particle size ofapproximately 100 microns.

In the water preparation phase, three preparations were made. First, alow oxygen fugacity, high pH water was obtained by adding sodiumbicarbonate and/or either sodium or potassium hydroxide to tap water inorder to adjust the pH of the water to three levels 8.3, 9.7, and 11.1.As understood by those skilled in the art, oxygen fugacity (fO₂) is ameasure of the amount of oxygen available to react with elements havingmultiple valence states—such as iron and carbon. A high oxygen fugacityis indicative of a high chemical potential of oxygen in the water. Alowered oxygen fugacity of water can be achieved or in a variety ofmanners (e.g., by the use of low oxygen fugacity water supply such asmunicipal wastewater, groundwater, mine water, or other wastewaterstream). One method for simply and reliably generating low oxygenfugacity water utilizes a heated bed of copper filings at 125° C.through which the water is passed to reduce the oxygen fugacity of thewater (i.e., decrease the amount of reactive oxygen in the water). Sucha method was used in this example implementation. Second, a saline waterwas obtained by adding salt (sodium chloride) to tap water to createsaline solutions ranging from 0.1 to 4.5 per mil. In preparation forcarbon mineralization experiments, the pH of the saline water wasadjusted to be between about 4.8 and about 6.5 using dilute HCl in amixture of distilled water and a sodium acetate buffer.

For the reaction process, a single batch reactor (made of 316 stainlesssteel) was designed and built to conduct the carbonation andserpentinization reactions in both batch and sequential configurations.All of the reactions were performed in this closed stainless steelreaction vessel as a “batch” reaction (i.e., closed system) with theexception of a fluid sampling port that was opened periodically. Foreach experiment, whole samples (approximately 250 grams) were selectedand sliced into two equally sliced approximately 125 grams of rawmaterial and then placed in the gas-tight, stainless steel reactionvessels. In preparation for the introduction of carbon dioxide to thevessel, distilled water was lightly acidified using dilute hydrochloricacid and a sodium acetate buffer, and then mixed with salt (sodiumchloride) to create a 0.1 to 4.5 per mil NaCl saline solution at ambientoxygen fugacity. This prepared water solution was then sprayed onto thepowdered rock introduced into the reactor vessel. The prepared watersolution provided a wet surface that enhanced the carbon dioxidereactivity with forsterite during the subsequent carbonation reactions.

In the first reaction phase, sequestration of carbon dioxide wastargeted through carbonation reactions between the introduced carbondioxide and the forsterite (and enstatite) in the ore. The acidic,saline water, prepared as described above, was applied to the powderedrock containing the forsterite mineral prior to placing the wetted(i.e., sprayed with water solution as described above) powdered rockinto the stainless-steel reaction vessel. Before the introduction ofcarbon dioxide, the reactor vessel was evacuated using a mechanicalrough pump to apply a vacuum and remove air from the reactor vessel,including ambient oxygen. Other embodiments involve flushing the vesselwith inert gas (e.g., N₂) or reaction gas (e.g., CO₂ or mixturesthereof) to remove air.

Next, either carbon dioxide gas or mixtures of carbon dioxide gas, e.g.,in a 4:1 ratio of carbon dioxide to nitrogen gas mixture, was introducedat room temperature and at an initial pressure of two bars (i.e., twiceatmospheric pressure); in another embodiment of this disclosure, otherratios of CO₂ to N₂ can be utilized. The carbon dioxide used was anultra-high purity carbon dioxide, such that the purity of carbon dioxidein the gas was greater than 99.9%, although mixtures with lower purityCO₂ can be utilized in various embodiments. The temperature inside thereactor vessel was then increased to 100° C., 150° C., 200° C., 250° C.,300° C., and 400° C. with the temperature being controlled by anexternal band heater and measured with a standard Omega K-wirethermocouple. At each temperature, the gas phase pressure was measuredvia the sampling port using a standard Omega 0 to 100 psi pressuregauge. At each temperature, an aliquot of gas measured using a StanfordResearch Systems residual gas analyzer (“quadrupole mass spectrometer”)and SRI gas chromatograph fitted with a thermocouple detector. The totalpressure of hydrogen was calculated by determining the product of thepercentage of hydrogen gas measured using the residual gas analyzerand/or gas chromatograph with the pressure compared to atmosphericpressure and assuming PV=nRT.

The kinetic rate of carbon mineralization appeared to increase by ˜1.6times when temperatures increased from 150° C. to 300° C., butadditional increases in the rate of CO₂ mineralization were notstatistically significant between 300° C. and 400° C. over reactiontimes of ˜18 hours in the batch experiments. Next, while holding aconstant temperature of 250° C., the pressure was increased to 5, 10,25, and 50 bars of carbon dioxide. At each step, the gas phase pressurevia the sampling port was monitored using a standard Omega 0 to 100 psipressure gauge on an attached expansion volume (to ensure the samplepressure was in the range of the available pressure gauge). For eachpressure, an aliquot of gas was also measured using an SRS quadrupolemass spectrometer and SRI gas chromatograph fitted with a thermocoupledetector after pressure reduction by expansion to a pre-evacuated samplechamber via the sampling port. The rate of carbon mineralization appearsto increase by ˜2.7 times between a pressure of 5 bars and 50 bars at250° C.

The preliminary results from the first reaction phase indicate that thekinetics of carbon dioxide mineralization increase with smaller grainsizes of the ore. There was a 23% improvement in the reduction of CO₂concentrations between 150 and 25 microns when holding temperatureconstant at 250° C., as determined based on CO₂ pressure andconcentration measurements and the mass of rock mineralized in thereaction vessel. While it is suspected that the removal of air willenhance the kinetics of carbon mineralization, at least one run withoutair/oxygen removal from the reactor vessel at the start of the firstreaction phase did not appear to noticeably affect the carbonizationreaction. Increasing both the temperature and the pressure of thereaction conditions increased the rate of CO₂ mineralization up throughat least 300° C. and 50 bars over reaction times of ˜18 hours in thebatch experiments. Based on the plateau in the pressure of the reaction,these conditions are assumed to approach thermodynamic equilibrium inbatch conditions between 12 and 18 hours, with variability observedthroughout various experimental conditions (i.e., generally less time athigher temperature and pressure).

During temperature increases from 100° C. to 300° C. at a constantpressure of 10 bars, the amount of mineralization increased from 14%additional mass (after 24 hours in a batch reactor) to 27%, representinga 92% increase in the mass of rock resulting from carbon mineralization.During pressure increases from 1 to 50 bar at a constant temperature of250° C., the amount of mineralization increased from 4.1% additionalmass (after 24 hours in a batch reactor) to 18.9%, representing a 4.6times increase in the mass of rock resulting from carbon mineralization.Rotary kiln, fluidized bed, and toroidal bed processes were notevaluated in this process, but can be expected to substantially increaseboth the reaction rates and total efficiency of mineralization ascompared to the batch process, even while temperature and pressureeffects are expected to be similar to those in the batch process.

In another experimental run, supercritical carbon dioxide was used inthe reactor during the first reaction phase. Preliminary resultsindicate that the supercritical CO₂ injected into the reactor at 10 barsand 250° C. reached a pressure plateau 4.5 hours (18.8%) faster thangaseous CO₂. Thus, the carbon sequestration from this disclosed ex situcarbonation reaction may be maximized or enhanced while accounting fortemperature and pressure in addition to other cost-intensive variables,such as energy input, material handling, and chemical processing costs.After the first reaction phase, the solid contents of the reactor wereweighed. Based on a mass increase of between 39.3 grams (15.7%) at 150°C. at 5 bar and 101.6 grams (40.6%) at 300° C. at 50 bar, the abundanceof total carbon mineralization was determined, which was verified usingoptical microscopy. Magnesite (i.e., magnesium carbonate), which was notobserved in the initial experimental material, was identified, asexpected based on the stoichiometry of the carbonation reactionresulting in a pre-concentration of an iron-rich iron-silica (fayaliteand/or ferrosilite) phase prior to the second reaction phase.

In the second reaction phase, liberation of the hydrogen was targetedthrough serpentinization/hydration reactions between the introducedwater and the fayalite and/or ferrosilite (mixture in the four naturalsamples and exclusively olivine one prepared sample) in the remainingore. Before the introduction of water with respect to theserpentinization reactions, the reactor vessel was evacuated using amechanical rough pump to apply a vacuum and remove air from the reactorvessel including any remaining introduced carbon dioxide. Next, lowoxygen fugacity (i.e., negative Eh value or negative electricpotential), high pH (i.e., pH ranging between 8.3 and 11.1 using sodiumbicarbonate or either sodium or potassium hydroxide), and saline (about0.1 to 4.5 per mil sodium chloride (NaCl)) water, prepared as describedabove, was then introduced at room temperature and ambient atmosphericpressure into reactor vessel containing the remaining ore (i.e.,unreacted ore consisting of the iron silicate phase, magnesiumcarbonate, silicon dioxide, residual olivine, pyroxene, and otheraccessory mineral phases).

The initial gas phase pressure was measured/recorded via the samplingport using the standard Omega 0 to 100 psi pressure gauge. Thetemperature inside the reactor vessel was then increased to 50° C., 100°C., 150° C., 200° C., 250° C., 300° C., and 400° C. with the temperaturebeing controlled by the external band heater and monitored with an OmegaK-wire thermocouple. At each temperature step, the gas phase pressurewas measured via the sampling port using the standard Omega 0 to 100 psipressure gauge. At each temperature, an aliquot of gas was measuredusing a Stanford Research Systems residual gas analyzer (“quadrupolemass spectrometer”) and SRI gas chromatograph fitted with a thermocoupledetector. The total pressure of hydrogen (and other gases) wascalculated by determining the product of the percentage of hydrogen gasmeasured using the residual gas analyzer and/or gas chromatograph withthe pressure compared to atmospheric pressure and assuming PV=nRT.

The preliminary results from the second reaction phase indicated thatthe kinetics of hydrogen evolution increase with smaller grain sizes ofthe ore. There was a 5.2 times improvement in the yield of H₂ betweenthe temperature steps of 50° C. and 100° C. when holding a constantpressure of 10 bars as determined based on H₂ partial pressure over atime interval of 18 hours. There was a 7.3 times improvement in theyield of H₂ concentrations between the temperature steps of 100° C. and400° C. when holding a constant pressure of 10 bars as determined basedon H₂ partial pressure over a time interval of 18 hours. The yield of H₂increased with pressure, but not to the same extent as temperature.There was a 31% times improvement in the yield of H₂ between 1 and 5bars at a constant temperature of 250° C., and a 1.8 times increase inthe yield of H₂ between 5 and 40 bars at a constant temperature of 250°C. as determined based on H₂ partial pressure over a time interval of 18hours. When compared to serpentinization reactions that were notpreceded by the two-step carbonation reaction, the kinetic rates of theserpentinization reaction increase by 21% at 150° C. and up to 87% at250° C. conducted at a constant pressure of 20 bars as compared toexperiments performed at 100° C. This change is believed to be due tothe carbonation-driven comminution of the ore that facilitated theinitial breakdown of the rock/ore as well as the pre-concentration ofthe iron silicate mineral phases. The highest increase in the yield ofH₂ was 1.8 times above the yield observed at 100° C. and was observed ata temperature step of 200° C. following density separation of SiO₂ andMgCO₃ from the denser iron silicates by laboratory sluicing; this stepyielded total H₂ production of 0.576 mol H₂/kg. Each increasingtemperature step demonstrated an improvement in the purity of thehydrogen gas evolved; variable mixtures of N₂, Ar and minor CO₂ wereobserved in both the 50° C. and 100° C. temperature steps, which wasless than 5% in the non-condensable fraction at temperatures above 150°C. with the exception of one sample at 400° C., which yielded 6.7% CO₂.

Along with the composition (%), the total pressure of the hydrogen gasthat was formed by the reaction increased with higher temperatures,indicating a progressive increase in the kinetic rates and the totalyield of hydrogen generation with higher temperature. Although thisresult was theoretically expected, it differentiates hydrogen producedby example embodiments described herein from hydrogen generated bynatural systems wherein the occurrence of CO₂, HCO₃ ⁻, or other forms ofcarbon in the subsurface can begin to react with hydrogen at ˜150° C.,which “short circuits” carbon-negative hydrogen generation by theformation of abiogenic methane via the Sabatier reaction (i.e.,CO₂+4H₂→CH₄+2H₂O), wherein CO₂ can be available as gaseous phase CO₂ orbe liberated from dissolved inorganic carbon phases in pore fluids bythe following reaction: H⁺HCO₃→CO₂+H₂O).

A comparison of the disclosed two-step reaction was performed by furthercomparison to two base case single step reactions. The first base casecomparison was a one-step reaction at a pH of 6.0 with temperaturesincreased from room temperature to 50° C., 100° C., 150° C., 200° C.,250° C., 300° C., and 400° C. The highest H₂ yield at this pH was lessthan 0.011 mol H₂/kg at 400° C., which was expected based on the mildlyacidic conditions. The second base case comparison was a one-stepreaction at a pH of 8.0 with temperatures increased from roomtemperature to 50° C., 100° C., 150° C., 200° C., 250° C., 300° C., and400° C. At this pH and holding pressure constant at 20 bars, H₂ yield inthe single step reaction ranged from below detection limits at 50° C. at18 hours to 0.051 mol H₂/kg at 100° C. and up to 0.349 mol H₂/kg at 400°C. For comparison, the highest value observed at the 400° C. in thesingle-step base case was 69.6% lower than the highest yield in thetwo-step reaction described above. Thus, the hydrogen gas productionfrom this disclosed ex situ serpentinization reaction may be maximizedor enhanced while accounting for temperature and pressure in addition toother cost-intensive variables, such as energy input, material handling,and chemical processing costs, especially by precluding interactionsbetween H₂ and labile carbon (i.e., CO₂).

After the sequential first and second reaction phases (i.e., thecarbonation and serpentinization reactions) were completed in thereaction vessel, the mass (i.e., weight), mineralogy, and geochemicalcomposition of the remaining bulk rock were determined by opticalmineralogy and ICP-MS to evaluate the abundance (or lack) of relevantconstituents (e.g., fayalite, ferrosilite, FeO, MgO, etc.). Whilevisible olivine and pyroxene were still observed along with minorserpentine, the amount of magnetite observed was significantly higher(11-171% based on the mass of the separatable magnetic components) inthe sequential reaction (i.e., first reaction phase followed by secondreaction phase) than when the reaction was done withoutpre-concentration of the fayalite and/or ferrosilite minerals andcontrol of reaction conditions, e.g., pH, low oxygen control,temperature. There was a 11% increase in the yield of magnetite betweenthe temperature steps of 50° C. and 100° C. and approximately 13%between 100° C. and 150° C., while there was 1.7 times more magnetiterecovered magnetically when comparing the 300° C. and 100° C. steps whenholding a constant pressure of 10 bars over a time interval of 18 hours.Based on the stoichiometry of the reactions and these observations, itis apparent that an increased generation of magnetite is coupled withand inextricably linked to an increased generation of hydrogen (as wasexpected from the stoichiometric serpentinization reaction). Theseresults support the stoichiometric modeling of both carbon dioxidemineralization (via carbonation) and hydrogen production (viaserpentinization/hydration reactions). Thus, magnetite may be producedas a co-product of hydrogen generation/evolution (or vice versa based onthe chosen business method).

Additional analysis of the residual material identified highly elevatedmetal enrichments that included phosphates, aluminum oxides, and otherpoorly defined solids in the gangue (“mineral slag”). For example,lanthanum (one rare earth element) demonstrated an average concentrationof 8.2 ppm in the bulk sample of ultramafic rock from the Pennsylvaniaquarry and 187.1 ppm in the residual gangue (largely aluminum oxide,phosphates and sulfides corresponding to roughly 2-4% of the totalmaterial). Similarly, nickel and cobalt concentrations were 133.9 and78.2 ppm in a bulk sample of ultramafic rock from the same Pennsylvaniaquarry and 1,426 and 976.8 ppm in the residual gangue (largely aluminumoxide and sulfides). Separation of these metal enrichments may beaccomplished by density separation techniques such as heavy liquidseparation or other gravity separation, or sluicing or other methodsknown to those skilled in the art.

The overall results indicate that, in the pursuit of carbon neutral oreven negative carbon hydrogen production, the sequential carbonation andserpentinization reactions phases disclosed herein provide severalreaction products (e.g., magnetite, rare earth elements, and otherscarce metals) of economic and societal value in the pursuit of a lowercarbon economy in addition to carbon sequestration and hydrogenevolution. Moreover, there exist a range of conditions where eachreaction may be enhanced that varies only slightly with different rockcontents, such that the reactions are more or less stable in theconditions described above among various sources of ultramafic and maficrocks.

As briefly discussed above, several reaction products have beenidentified from the staged, sequential carbonation and serpentinizationreactions disclosed herein. Four reaction products in particular havethe potential to be economically viable, especially when enhanced orenabled by steps, procedures, reaction conditions described herein thatenhance the rock comminution and thermodynamic drivers toward idealized“carbonation” and serpentinization/hydration reactions. Adding to theireconomic viability, there may be revenue entitlements tied to theproduction of these reaction products, such as tax credits, sale ofcarbon credits, tax incentives, etc. The four products include:magnesite/aggregate, “green” or “golden” hydrogen (net carbon negative),magnetite, and scarce metals, and each will be discussed furtherhereinbelow.

Magnesite

The controlled ex situ generation of magnesite (magnesium carbonate) byenhancing “water-rock” serpentinization/hydration reactions involvingmined, quarried, or waste (e.g., mine tailings) mafic or ultramafic rockand products provides an economic and carbon neutral (or even carbonnegative) pathway for scalable magnesite and rock aggregate formation.This process can also economically increase the volume and mass of therock (stoichiometric assessment of suitable mafic/ultramafic oressuggest the mass can increase by 34 to >60% (or 0.34 to >0.60 kg/kg ofrock or 340 kg to >600 kg/metric ton of rock), while experimentalresults suggested at increase of 0.104 kg/kg (300° C. at 50 bars in thebulk rock obtained from the Pennsylvania quarry) to 0.237 kg/kg (300° C.at 50 bars in the pure olivine test sample). These values are expectedto increase further by moving from a batch to dynamic reaction process(e.g., rotary kiln, fluidized bed, toroidal bed, or other similarprocesses) of rock compared to the original material introduced into thebatch reactor.

As disclosed, water having a pH of between about 4.8 to about 6.5 may bemixed with carbon dioxide in controlled conditions (e.g., underatmospheric or oxidizing conditions) to chemically break down themagnesium-rich silicate (i.e., forsterite) portion of mafic andultramafic rocks. This reaction may be enhanced at temperatures ofbetween about 150° C. to about 300° C. to 400° C. (although ourexperiment displayed a plateau in increased mineralization at 300° C.)and at pressures of at least up to 50 bars to produce magnesite. Thiscarbonation process permanently sequesters carbon dioxide through theprecipitation of magnesite mineral phases and other carbonate minerals,which can be used directly or as rock aggregate.

The successful conversion of magnesium-silicate into magnesium carbonateand other carbonate minerals also allows the possibility to remove thebulk of the rock mass (following previously described density separationtechniques) that can subsequently be either separated from residualiron-silicates or be separated prior to serpentinization/hydrationreactions. The step of concentrating the iron silicate phase can furtherconcentrate scarce metals (e.g., nickel, cobalt, rare earth elements) inother mineral forms (e.g., aluminum oxides, phosphates, and sulfides).This carbonation process is conducted first such that sequentialserpentinization reactions may more readily and abundantly produce thereaction products of magnetite and hydrogen gas without the formation ofaccessory/competitive phases and enhance comminution.

The importance of scalable and carbon negative (or carbon neutral)magnesium carbonate (magnesite) production has direct bearing on thenumerous current uses of magnesite, including, but not limited to,pharmaceutical applications, agricultural lime and fertilizers (toneutralize acidification caused by fertilizer use), raw materials forceramic and ceramic brick, and flux used in iron and steelmanufacturing. Magnesite may also be used as a partial lime substituteto enable lower carbon emissions that result from the lower temperaturesrequired to make magnesium oxide (MgO) as compared to calcium oxide(CaO). Further, magnesite can be used as a carbon negative concretefiller and cement or aggregate substitute in concrete.

Green/Golden Hydrogen

Hydration reactions involving iron-silicates (e.g., fayalite,ferrosilite) may be used to generate “green” (i.e., carbon neutral) or“golden” (i.e., carbon negative) hydrogen ex situ from mined, quarried,or waste streams of olivine- and/or pyroxene-rich ores, such as maficand ultramafic rock. In one or more embodiments of the systems andmethod disclosed herein, the ex situ generation of carbon-negativehydrogen is directed to a two-reaction step/phase process in which: (1)carbon dioxide is first introduced in a gaseous or supercritical stateinto pulverized rock (approximately <150 microns) that has been wettedwith a water preparation having a pH of between about 4.8 and about 6;and (2) water with a low oxygen fugacity (e.g., obtained from municipalwastewater, geothermal water, or other industrial water uses or made byreacting tap water over a bed of copper at 125° C.), a pH of between 8.3and about 11.1 (the specified pH attained by adding sodium bicarbonateor either sodium or potassium hydroxide to the water but such water pHmay be found in natural sources of water and wastewater) across atemperature range of between about 60° C. and about 400° C.

The removal of a substantial portion of magnesium component from thepowdered or comminuted rock in the first reaction phase increases thechemical (reaction) potential of the iron-rich portion in the secondreaction phase. Stoichiometric calculations suggest that the chemicalactivity can be increased by up to eight times, while improvements ofapproaching a factor of two were observed in experiments; it isanticipated that the chemical activity and kinetics can be furtherincreased by transitioning from a batch to dynamic process. Indeed, therates of hydrogen production are significantly greater (nearly 70%greater) than in a method in which the iron-rich silicate mineral isreacted without the precursor step of carbon dioxide mineralizationcompared to a suitable base case for natural reactions or other one stepengineered reaction processes.

A significant advantage of various embodiments disclosed herein is thatthe systems and methods of such embodiments can be set up for ex situoperation almost anywhere in the world due to the vast and far-reachingreserves of mafic and ultramafic rock and availability of water andchemicals for amendment of pH and Eh of the water. Conversely, hydrogenformation in a more conventional manner, such as by natural gasreforming, is limited by natural gas availability, among otherconstraints that are often carbon intensive. Even if the produced carbondioxide is sequestered, the hydrogen would be considered “blue,” not“green” or “golden.”

Magnetite

The controlled ex situ generation of magnetite by enhancing “water-rockserpentinization” reactions on mined, quarried, or waste streams ofolivine- and/or pyroxene-rich ores and other materials provides aneconomic and carbon neutral (or even carbon negative) pathway for theproduction of magnetite while also enabling commensurate carbon dioxidesequestration through carbonate mineralization. While carbonation andserpentinization reactions are themselves naturally occurring,embodiments of the systems and methods disclosed herein are directed toenhanced magnetite production through the sequential ordering of thesereactions in a controlled ex situ environment to limit alternative andundesirable chemical reactions capable of producing serpentine, brucite,or asbestos.

In various embodiments disclosed herein, the ex situ generation ofmagnetite is directed to a two-reaction step/phase process in which: (1)carbon dioxide is first introduced in a gaseous or supercritical statein the presence of pulverized rock (approximately <150 microns) that hasbeen wetted with a water preparation having a pH of between about 4.8and about 6.5; and (2) water with a low oxygen fugacity (e.g., obtainedfrom municipal wastewater, geothermal water, treated groundwater orother industrial water uses or made by reacting tap water over a bed ofcopper at 125° C.) having a pH of between 8.3 and about 11.1 (thespecified pH attained by adding sodium bicarbonate or either sodium orpotassium hydroxide to the water but such water pH may be found innatural sources of water and wastewater) is introduced across atemperature range of between about 80° C. and about 400° C. The two-stepreaction at temperature >300° C. improves magnetite recovery by ˜1.7times compared to lower temperatures and a suitable base case. Further,removal of a substantial portion of magnesium component from thepowdered or comminuted rock in the first reaction step/phase increasesthe chemical (reaction) potential of the iron-rich portion in the secondreaction step/phase (e.g., by approximately 23-800%), thereby increasingthe thermodynamic drivers of magnetite generation several times. Thus,the generation of preferred mineral products, such as magnetite andhydrogen, is increased when compared to the random or undesired mineralspecies typically generated in natural systems. Indeed, the rates ofmagnetite production are significantly greater, and the targetedproduction of these specific chemical species is more reliable (e.g.,the formation of serpentine, brucite, or asbestos are reduced) than in amethod in which the iron-rich silicate mineral is reacted without theprecursor step of carbon dioxide mineralization or in which both CO₂ andwater are reacted together (which occurs in natural systems).

The Direct Reduction Iron (DRI) process is the only commercial lowcarbon emissions iron making process, and it is a precursor to steelmanufacturing. The DRI process requires high-grade iron ore (greaterthan approximately 67% iron), which is in short supply in natural ironores worldwide. Such limited access to magnetite (or other similarlyiron-rich mineral phases) limits the potential to produce iron or steelusing the DRI process, which is an important pathway for reducing carbondioxide emissions in the steel industry. The systems and methodsdisclosed herein may produce high-grade iron ore (magnetite) in vastquantities due to the prolific occurrence of mafic and ultramafic rock,which accounts for greater than 10% of the continental crust and thevast majority of the oceanic crust. Moreover, the carbon dioxidesequestration tax credits and/or carbon credit sales associated withmagnesite production may be attached to the magnetite output of thesesystems and methods. Thus, embodiments disclosed herein may increase theavailability of high-grade iron ore to the steel industry along with acarbon credit, which may also result in the “greening” of the steelindustry worldwide. Notably, the collective co-production (at onephysical site) of magnesite, magnetite, and hydrogen gas also satisfiesthree requirements (i.e., iron-rich iron ore; reductive gasspecies/hydrogen; and magnesite flux) of iron making processes.

Scarce Metals

Elevated concentrations of certain relatively scarce metals (e.g.,nickel, cobalt, chromium, and rare earth elements) in mafic andultramafic rocks may be liberated and more easily recovered ex situthrough sequential carbon sequestration/carbonation and “water-rock”serpentinization reactions involving mined, quarried, or waste mafic orultramafic rock/ore. These scarce, and in some cases strategic, metalsare critical for renewable energy and energy storage and are oftenderived from mining of weathered or processed minerals in more energyintensive steps (i.e., dehydration of asbestos back to forsterite).However, the disclosed system and method provides an economic and carbonneutral (or even carbon negative) pathway for the production of thesescarce metals, while also enabling carbon sequestration bymineralization of carbon dioxide. The reaction of gaseous orsupercritical carbon dioxide with forsterite chemically breaks downthese magnesium-rich silicate minerals and simultaneously sequesterscarbon from carbon dioxide, while the reaction of water with fayaliteand/or ferrosilite chemically breaks down the iron-rich silicateminerals and simultaneously produces magnetite and hydrogen gas. Withthe breakdown of these minerals, the remaining scarce metals areconcentrated in the remaining unreacted ore and gangue (i.e.,aluminosilicates, phosphates, accessory oxides, clay, etc.). Thus, thekinetic rates of the reactions of one or more embodiments disclosedherein and total metal recovery (i.e., higher concentrations in thestarting composition) are much increased over natural chemicalweathering of mafic and ultramafic rock. Further, the concentration ofscarce metals is increased in the gangue, and the carbon footprint of“mining” or recovering these precious metals (and their derivativeutilization in mobility and energy storage) is reduced. Therefore, thesequential carbonation and serpentinization reactions may provide forwhat is, in essence, a carbon negative mining of scarce and strategicmetals.

CONCLUSION

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments in the context of certain examplecombinations of elements and/or functions, it should be appreciated thatdifferent combinations of elements and/or functions may be provided byalternative embodiments without departing from the scope of the appendedclaims. In this regard, for example, different combinations of elementsand/or functions than those explicitly described above are alsocontemplated as may be set forth in some of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A method for sequestering carbon and generatinghydrogen and magnetite from rock, the method comprising: obtaining anore containing olivine or pyroxene; introducing the ore into a reactorthat is operable at temperatures above ambient temperature and pressuresabove atmospheric pressure; introducing carbon dioxide into the reactorat a first temperature for a first residence time to react with the oreto generate magnesium carbonate; introducing water into the reactor at asecond temperature for a second residence time to react with the ore togenerate magnetite and hydrogen gas; removing the hydrogen gas from thereactor; and removing any remaining ore from the reactor.
 2. The methodof claim 1, further comprising comminuting the ore into smaller sizefractions prior to introducing the carbon dioxide into the reactor. 3.The method of claim 2, further comprising washing the ore with eitherwater or an acidic solution prior to comminuting the ore into thesmaller size fractions.
 4. The method of claim 1, further comprisingremoving at least a portion of the magnesium carbonate from the reactorprior to introducing the water into the reactor.
 5. The method of claim1, wherein the water has a pH of between about 8.3 and about 11.1;wherein the carbon dioxide that is introduced into the reactor isgaseous or supercritical carbon dioxide; or wherein at least one of thefirst temperature and the second temperature is no greater than 300° C.6. The method of claim 1, further comprising: passing the water througha heated bed of copper filings to reduce an oxygen fugacity of the waterprior to introducing the water into the reactor; applying, prior tointroducing the carbon dioxide into the reactor, an acidic solution tothe ore that is introduced into the reactor; or removing oxygen from thereactor prior to introducing the carbon dioxide into the reactor.
 7. Themethod of claim 1, further comprising separating at least one of nickel,cobalt, lithium, chromium, or rare earth elements from the remainingore.
 8. A method for sequestering carbon and generating hydrogen andmagnetite from rock, the method comprising: obtaining an ore containingolivine or pyroxene; introducing the ore into a first reactor that isoperable at temperatures above ambient temperature and pressures aboveatmospheric pressure; introducing carbon dioxide into the first reactorat a first temperature for a first residence time to react with the oreto generate magnesium carbonate; passing any remaining ore to a secondreactor; introducing water into the second reactor at a secondtemperature for a second residence time to react with the remaining oreto generate magnetite and hydrogen gas; removing the hydrogen gas fromthe second reactor; and removing any remaining ore from the secondreactor.
 9. The method of claim 8, further comprising: sieving the oreprior to introducing the ore into the first reactor to allow oreparticles up to a pre-selected size to pass into the first reactor,wherein introducing the ore into the first reactor comprisesintroducing, into the first reactor, only a subset of the ore havingparticles up to the pre-selected size.
 10. The method of claim 9,wherein the pre-selected size comprises a size of between about 25microns and about 150 microns.
 11. The method of claim 8, wherein thewater has a pH between about 8.3 and about 11.1.
 12. The method of claim8, further comprising passing the water through a heated bed of copperfilings to reduce an oxygen fugacity of the water prior to introducingthe water into the second reactor.
 13. The method of claim 8, wherein atleast one of the first temperature and the second temperature is nogreater than 400° C.
 14. The method of claim 8, wherein a pressureinside the first reactor during the first residence time is at or aboveabout 5 bars of carbon dioxide.
 15. The method of claim 8, wherein apressure inside the second reactor during the second residence time isat or above about 1 bar of carbon dioxide.
 16. The method of claim 8,further comprising: washing the ore with either water or an acidicsolution prior to introducing the carbon dioxide into the first reactor;and sieving the ore prior to introducing the ore into the first reactorto allow ore particles up to a pre-selected size to pass into the firstreactor, wherein introducing the ore into the first reactor comprisesintroducing, into the first reactor, only a subset of the ore havingparticles up to the pre-selected size, wherein the pre-selected sizecomprises a size of between about 25 microns and about 150 microns. 17.The method of claim 16, wherein the water has a pH of between about 8.3and about 11.1.
 18. A system for sequestering carbon and producinghydrogen and magnetite from rock, the system comprising: a source of orecontaining olivine or pyroxene; a reactor having an inlet that receivesore particles and at least one outlet, the reactor also having at leastone additional inlet through which one or more of carbon dioxide orwater is introduced, the reactor operable at a first temperature for afirst residence time to react carbon dioxide that enters the reactorthrough the at least one additional inlet with the ore to generatemagnesium carbonate, the reactor also operable at a second temperaturefor a second residence time to react water that enters the reactorthrough the at least one additional inlet with the ore to generatemagnetite and hydrogen gas; and a gas separator that is connected to andin fluid communication with the at least one outlet of the reactor, thegas separator configured to separate hydrogen gas from gases that exitthe reactor through the at least one outlet.
 19. The system of claim 18,further comprising a crusher that physically reduces a particle size ofthe ore introduced therein from the source.
 20. The system of claim 19,further comprising: a sieve that receives ore from the crusher and thatallows ore particles up to a pre-selected size to pass into the reactor,wherein the inlet that receives ore particles is configurable to onlyreceive, from the sieve, ore particles having a size at or below to thepre-selected size; and a magnetic separator that receives any remainingore from the at least one outlet of the reactor, the magnetic separatorhaving a magnet that attracts the magnetite and thereby separates themagnetite from other components of the remaining ore.